Allow recalculating representative docs with a configurable count (currently hardcoded to 3)

[pidefrem]

Feature request

_save_representative_docs hardcodes nr_samples=500 and nr_repr_docs=3. Users cannot control how many representative documents are stored per topic, nor the sampling pool size.

Add a public method to recalculate representative documents after training with a configurable count, following the API direction suggested in #1767:

# Recalculate with more representative docs after training
topic_model.recalculate_representative_docs(nr_repr_docs=10, nr_samples=1000)

Motivation

This is a frequently requested feature:

• #552 — "get more than 3 representative docs"
• #848 — "Ability to change # of documents pulled per topic"
• #1767 — "How to get more than 3 representative docs per topic"

In #1767, @MaartenGr noted:

"It might be nice to have an additional function that re-calculates the representative documents since this question seems to appear frequently."

PR #2130 attempted an nr_repr_docs constructor parameter, but @MaartenGr's feedback was that he prefers a standalone public function that recalculates representative docs after training.

Use cases: production users who need more docs for human review, small datasets where 500 exceeds topic size, users who want to iterate on representative doc quality post-training.

Your contribution

I can submit a PR following @MaartenGr's preferred API direction:

1. New public method: recalculate_representative_docs(nr_repr_docs=3, nr_samples=500) — recalculates and replaces representative_docs_ after training.
2. Constructor defaults nr_repr_docs (default 3) and nr_repr_docs_nr_samples (default 500) — used during fit_transform().

I've already been prototyping this in my fork along the lines you suggested, so I can open a PR quickly if this direction works for you.

Backward compatible: defaults reproduce the current behavior exactly.

Note: Works standalone. Pairs well with the sampling/indexing fix for _extract_representative_docs (#2495) — that fix corrects the sampling this method configures.

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